1. Field of the Invention
This invention relates to pumps, for example for incorporation in dip-tube sprayers.
2. Description of the Prior Art
At the present time pumps are known which comprise a hollow piston slidably mounted in a cylinder communicating with an outlet tube with which it is coaxial, and forming a seat for a valve which, at rest, is held by a spring against the piston, the communication between the cylinder and the tube thus being interrupted, and can be changed over to an open position by axial displacement of the tube.
In one such pump, the outlet tube is rigid with the valve and is movable, over a limited distance, with respect to the piston. In order to operate the pump, the tube is displaced towards the cylinder which initially drives the valve thereby displacing it from its seat, then the piston which delivers the liquid contained in the cylinder to the tube.
This pump however gives rise to certain disadvantages, in particular when it is incorporated in a dip-tube sprayer in which the outlet tube is connected to an atomizing nozzle. In practice, if the tube is displaced slowly, the delivery pressure is initially very low and the atomization is poor; it may even happen that the liquid only leaves the nozzle in the form of a broken up jet.
An object of the present invention is to provide an improved pump suitable for incorporation in a dip-tube sprayer.